Osteochondroma is the most common benign tumor of bone arising from the metaphysis of long bone in a growing child. Osteochondroma arising from the epiphysis are rare. Misplacement of epiphyseal cartilage cells or perichondrial cells have been proposed as the cause for osteochondroma but the cause for this in normal humans remains largely unknown. In literature only few cases of solitary epiphyseal osteochondroma have been reported.[1],[2],[3] We present a case of epiphyseal osteochondroma presenting very early with mechanical symptoms, its differential diagnoses and its management.

Case Report

An 18 months female child presented with swelling near left knee joint for 8 months with insidious onset and gradual increase in size. There was no history of fever or injury around knee joint. On examination there was a round bony hard swelling of about 2 cm in front of knee joint in between the patellar tendon and inferior pole of the patella [Figure 1(a)]. Swelling was smooth, non-tender and immobile. Range of movement of the knee was normal and there was no limb length discrepancy. A careful survey of the whole body did not reveal any other similar swelling. Contralateral knee and both ankles also had normal range of motion.

X-ray revealed a rounded bony mass in front of the proximal tibial epiphysis. The epiphysis itself and the joint were otherwise normal. The X-rays taken at the age of 10 months and 18 months clearly showed the increase in size of the lesion with the growth of the limb [Figure 1(b)],[Figure 1(c)].

Under anaesthesia, through midline skin incision and patellar tendon splitting incision, the tumor was approached. A 2 X 3 cm bony mass with smooth glistening surface was found in the retropatellar region attached to the tibial epiphysis in the intracapsular and extra synovial region. The tumor did not have any connection with the patellar ligament. The tumor was excised at its base and patellar tendon sutured [Figure 2(a)],[Figure 2(b)]. Histopathology showed mature bony trabeculae capped by cartilaginous cells confirming the diagnosis of osteochondroma [Figure 2(c)].

Discussion

Typical osteochondroma are derived from aberrant cartilaginous epiphyseal growth plate tissue, which proliferates autonomously and separates from the normal growth plate near its edge.[4] As growth progresses, the aberrant tissue remains in a subperiosteal location, where it may either disappear through remodeling or proliferate as an early osteochondroma perpendicular to the orientation of the growth plate from which it was derived. Experimentally osteochondroma can also be developed from perichondrial ring cells by reflection of perichondrial ring.[5] The factors that influence this misplacement of epiphyseal cartilage cells or perichondrial cells in normal humans remains largely unknown. Epiphyseal osteochondroma may represent those cases where the epiphyseal plate cartilage is displaced and misplaced towards the epiphysis.

In literature only few cases of solitary epiphyseal osteochondroma have been reported. Chekofsky et al demonstrated an osteochondroma growing from the tibial epiphysis into the anterior cruciate ligament in 8 year old boy who had pain, swelling and restricted knee motion.[1] According to them, epiphyseal osteochondroma should be added to the working differential diagnosis in children with effusion and decrease of knee motion. Calabet et al reported two cases of epiphyseal osteochondroma arising from proximal tibial epiphyses with intraarticular development. One patient had restricted knee motion while the other had asymptomatic knee.[2] They noticed talar osteochondroma in one of their two cases, which necessitated surgical resection. Laflamme et al reported solitary epiphyseal osteochondroma in the phalanges of seven children.[3] All patients presented with a progressive angular deformity leading to limited function of the hand. Five patients had limited range of motion. Good restoration of motion and function was achieved by excision of the lesion and collateral ligament reconstruction.

Because of close proximity to joint epiphyseal osteochondroma are noticed earlier than the typical metaphyseal osteochondroma. Our case was only 18 months old and the lesion was noticed since the age of 10 months. This is probably the youngest case with solitary epiphyseal osteochondroma. The frequency of pain, joint effusion and decreased range of motion because of intraarticular development is common with this condition.

Before reaching the diagnosis of solitary epiphyseal osteochondroma, Trevor's disease has to be excluded. Trevor's disease or dysplasia epiphysealis hemimelica is a developmental disorder characterized by asymmetric enlargement of multiple epiphyses.

The disorder most commonly affects distal femur, proximal tibia, distal tibia and talus. Trevor's disease is thought to be the result of fusion in the growth plate of isolated irregular centers of ossification leading to asymmetric enlargement of epiphysis, the resulting mass resembling osteochondroma.[6] Deformities, limb length discrepancy, decreased range of motion and functional impairment are common in this condition.

In conclusion, the possibility of solitary epiphyseal osteochondroma should be kept in mind for any bony lesion close to the joint, especially in a young child. Early excision of the lesion is recommended to avoid intra-articular development and mechanical block to joint motion.